<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    div{
      color: red;
    }
    .one{
      color: green;
    }
    .two{
      font-size: 50px;
    }
    #world{
      color: blue;
      font-size: 100px;
    }


  </style>

</head>
<body>
<!-- 希望第一个div和第三个div是绿色 -->
<div class="one">hello</div>
<div id="world">world</div>
<div class="one two">java</div>

</body>
</html>